To conduct seismic exploration of water-covered areas of the earth, the usual practice is to tow a streamer cable through the water behind a vessel. The cable has a plurality of spaced-apart hydrophone detectors that sense the arrival of acoustic waves and provide electrical output signals that are indicative thereof. Periodic seismic disturbances are created in the water in the vicinity of the cable through operation of air guns, gas guns, sparkers, or even dynamite or the like, so that acoustic waves are created which travel downward through the earth. At subterranean levels where there are substantial changes in rock density, a portion of the wave is reflected back upward and is detected by the hydrophones. Electrical signals from the phones are transmitted via a bundle of conductor wires extending axially within the streamer cable to data processing and recording equipment onboard the vessel.
In modern seismic practices, streamer cables have become quite lengthy. It is not uncommon for a cable to be 2-3 miles long and comprise about 240-300 information channels. Each phone, or a discrete group of phones, is connected to onboard equipment using a pair of insulated conductor wires, so that it can be readily appreciated that a sizable bundle of such wires must be contained within the cable. A bundle that has in excess of 300 pairs of conductor wires is not unusual.
The towing load on each cable section typically is carried by three circumferentially spaced wire ropes that extend through spaced bulkheads and have their ends attached to connector fittings at the opposite ends of each section. The wire ropes are formed of twisted strands of wire that present rough and abrasive exterior surfaces. Inasmuch as the wire ropes extend alongside the conductor wire bundle, the ropes can rub against the conductor wires during handling and use, causing disruptions in the wire insulation and shorting. Of course when this happens, the conductor pair in which the shorted wire is located becomes inoperable and incapable of functioning to transmit signals from the phone or group of phones to which it is connected. That channel is dead.
The general object of the present invention is to provide a new and improved marine streamer cable section having sheaths that provide a protection for the conductor wire bundle against abrasion and damage caused by rubbing thereof against the wire rope strain members of the cable.